import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main2 {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[] dp = new int[n+1];
        dp[1] = 1;
        if(n < 2) {
            System.out.println(dp[n]);
            return;
        }
        dp[2] = 2;
        for(int i = 3; i <= n; i++) {
            dp[i] = dp[i-1] + dp[i-2];
        }
        System.out.println(dp[n]);
    }
}